Internet Engineering Task Force (IETF) T. Schmidt, Ed.
Request for Comments: 7287 HAW Hamburg
Category: Experimental S. Gao
ISSN: 2070-1721 H. Zhang
Beijing Jiaotong University
M. Waehlisch
link-lab & FU Berlin
June 2014
Mobile Multicast Sender Support in Proxy Mobile IPv6 (PMIPv6) Domains
Abstract
Multicast communication can be enabled in Proxy Mobile IPv6 (PMIPv6)
domains via the Local Mobility Anchors by deploying Multicast
Listener Discovery (MLD) proxy functions at Mobile Access Gateways,
by using direct traffic distribution within an ISP's access network,
or by selective route optimization schemes. This document describes
a base solution and an experimental protocol to support mobile
multicast senders in PMIPv6 domains for all three scenarios.
Protocol optimizations for synchronizing PMIPv6 with PIM, as well as
a peering function for MLD proxies are defined. Mobile sources
always remain agnostic of multicast mobility operations.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). It represents the consensus of the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are a candidate for any level of
Internet Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7287.
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Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
3. Base Solution for Source Mobility and PMIPv6 Routing . . . . 5
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Base Solution for Source Mobility: Details . . . . . . . 9
3.2.1. Operations of the Mobile Node . . . . . . . . . . . . 9
3.2.2. Operations of the Mobile Access Gateway . . . . . . . 9
3.2.3. Operations of the Local Mobility Anchor . . . . . . . 9
3.2.4. IPv4 Support . . . . . . . . . . . . . . . . . . . . 10
3.2.5. Efficiency of the Distribution System . . . . . . . . 11
4. Direct Multicast Routing . . . . . . . . . . . . . . . . . . 12
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. MLD Proxies at MAGs . . . . . . . . . . . . . . . . . . . 13
4.2.1. Considerations for PIM-SM on the Upstream . . . . . . 14
4.2.2. SSM Considerations . . . . . . . . . . . . . . . . . 14
4.3. PIM-SM at MAGs . . . . . . . . . . . . . . . . . . . . . 15
4.3.1. Routing Information Base for PIM-SM . . . . . . . . . 15
4.3.2. Operations of PIM in Phase One (RP Tree) . . . . . . 16
4.3.3. Operations of PIM in Phase Two (Register-Stop) . . . 16
4.3.4. Operations of PIM in Phase Three (Shortest-Path Tree) 17
4.3.5. PIM-SSM Considerations . . . . . . . . . . . . . . . 18
4.3.6. Handover Optimizations for PIM . . . . . . . . . . . 18
4.4. BIDIR-PIM . . . . . . . . . . . . . . . . . . . . . . . . 18
4.4.1. Routing Information Base for BIDIR-PIM . . . . . . . 19
4.4.2. Operations of BIDIR-PIM . . . . . . . . . . . . . . . 19
5. MLD Proxy Peering Function for Optimized Source Mobility in
PMIPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 20
5.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 20
5.3. Operations in Support of Multicast Senders . . . . . . . 20
5.4. Operations in Support of Multicast Listeners . . . . . . 21
6. Security Considerations . . . . . . . . . . . . . . . . . . . 23
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.1. Normative References . . . . . . . . . . . . . . . . . . 24
8.2. Informative References . . . . . . . . . . . . . . . . . 24
Appendix A. Multiple Upstream Interface Proxy . . . . . . . . . 26
A.1. Operations for Local Multicast Sources . . . . . . . . . 26
A.2. Operations for Local Multicast Subscribers . . . . . . . 26
Appendix B. Implementation . . . . . . . . . . . . . . . . . . . 27
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1. Introduction
Proxy Mobile IPv6 (PMIPv6) [RFC5213] extends Mobile IPv6 (MIPv6)
[RFC6275] by network-based management functions that enable IP
mobility for a host without requiring its participation in any
mobility-related signaling. Additional network entities called Local
Mobility Anchor (LMAs) and Mobile Access Gateways (MAGs) are
responsible for managing IP mobility on behalf of the mobile node
(MN). An MN connected to a PMIPv6 domain, which only operates
according to the base specifications of [RFC5213], cannot participate
in multicast communication, as MAGs will discard group packets.
Multicast support for mobile listeners can be enabled within a PMIPv6
domain by deploying MLD proxy functions at Mobile Access Gateways,
and multicast routing functions at Local Mobility Anchors [RFC6224].
This base deployment option is the simplest way to PMIPv6 multicast
extensions in the sense that it follows the common PMIPv6 traffic
model and neither requires new protocol operations nor additional
infrastructure entities. Standard software functions need to be
activated on PMIPv6 entities, only, at the price of possibly non-
optimal multicast routing.
Alternate solutions leverage performance optimization by providing
multicast routing at the access gateways directly [MULTI-EXT] or by
using selective route optimization schemes [RFC7028]. Such
approaches (partially) follow the model of providing multicast data
services in parallel to PMIPv6 unicast routing [RFC7161].
Multicast listener support satisfies the needs of receptive use cases
such as IPTV or server-centric gaming on mobiles. However, current
trends in the Internet develop towards user-centric, highly
interactive group applications like user-generated streaming,
conferencing, collective mobile sensing, etc. Many of these popular
applications create group content at end systems and can largely
profit from a direct data transmission to a multicast-enabled
network.
This document describes the support of mobile multicast senders in
Proxy Mobile IPv6 domains for the base deployment scenario [RFC6224],
for direct traffic distribution within an ISP's access network, as
well as for selective route optimization schemes. The source
mobility problem as discussed in [RFC5757] serves as a foundation of
this document. Mobile nodes in this setting remain agnostic of
multicast mobility operations.
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2. Terminology
This document uses the terminology as defined for the mobility
protocols [RFC6275], [RFC5213], and [RFC5844], as well as the
multicast routing [RFC4601] and edge-related protocols [RFC3376],
[RFC3810], and [RFC4605].
Throughout this document, we use the following acronyms:
HNP Home Network Prefix as defined in [RFC5213].
MAG Mobile Access Gateway as defined in [RFC5213].
MLD Multicast Listener Discovery as defined in [RFC2710] and
[RFC3810].
PIM Protocol Independent Multicast as defined in [RFC4601].
PMIPv6 Proxy Mobile IPv6 as defined in [RFC5213].
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Base Solution for Source Mobility and PMIPv6 Routing
3.1. Overview
The reference scenario for multicast deployment in Proxy Mobile IPv6
domains is illustrated in Figure 1. It displays the general setting
for source mobility -- mobile nodes (MNs) with Home Network Prefixes
(HNPs) that receive services via tunnels, which are spanned between a
Local Mobility Anchor Address (LMAA) and a Proxy Care-of-Address
(Proxy-CoA) at a Mobility Access Gateway (MAG). MAGs play the role
of first-hop access routers that serve multiple MNs on the downstream
while running an MLD/IGMP proxy instance for every LMA upstream
tunnel.
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+-------------+
| Multicast |
| Listeners |
+-------------+
|
*** *** *** ***
* ** ** ** *
* *
* Fixed Internet *
* *
* ** ** ** *
*** *** *** ***
/ \
+----+ +----+
|LMA1| |LMA2| Multicast Anchor
+----+ +----+
LMAA1 | | LMAA2
| |
\\ //\\
\\ // \\
\\ // \\ Unicast Tunnel
\\ // \\
\\ // \\
\\ // \\
Proxy-CoA1 || || Proxy-CoA2
+----+ +----+
|MAG1| |MAG2| MLD Proxy
+----+ +----+
| | |
MN-HNP1 | | MN-HNP2 | MN-HNP3
| | |
MN1 MN2 MN3
Multicast Sender + Listener(s)
Figure 1: Reference Network for Multicast Deployment in PMIPv6
An MN in a PMIPv6 domain will decide on multicast data transmission
completely independent of its current mobility conditions. It will
send packets as initiated by applications, using its source address
with an HNP and a multicast destination address chosen by application
needs. Multicast packets will arrive at the currently active MAG via
one of its downstream local (wireless) links. A multicast-unaware
MAG would simply discard these packets in the absence of instructions
for packet processing, i.e., a Multicast Routing Information Base
(MRIB).
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An MN can successfully distribute multicast data in PMIPv6, if MLD
proxy functions are deployed at the MAG as described in [RFC6224].
In this setup, the MLD proxy instance serving a mobile multicast
source has configured its upstream interface at the tunnel towards
the MN's corresponding LMA. For each LMA, there will be a separate
instance of an MLD proxy.
According to the specifications given in [RFC4605], multicast data
arriving from a downstream interface of an MLD proxy will be
forwarded to the upstream interface and to all but the incoming
downstream interfaces that have appropriate forwarding states for
this group. Thus, multicast streams originating from an MN will
arrive at the corresponding LMA and directly at all mobile receivers
co-located at the same MAG and MLD proxy instance. Serving as the
designated multicast router or an additional MLD proxy, the LMA
forwards data to the fixed Internet, whenever forwarding states are
maintained by multicast routing. If the LMA is acting as another MLD
proxy, it will forward the multicast data to its upstream interface
and to downstream interfaces with matching subscriptions,
accordingly.
In case of a handover, the MN (being unaware of IP mobility) can
continue to send multicast packets as soon as network connectivity is
re-established. At this time, the MAG has determined the
corresponding LMA, and IPv6 unicast address configuration (including
PMIPv6 bindings) has been completed. Still, multicast packets
arriving at the MAG are discarded (if not buffered) until the MAG has
completed the following steps.
1. The MAG has determined that the MN is admissible to multicast
services.
2. The MAG has added the new downstream link to the MLD proxy
instance with an uplink to the corresponding LMA.
As soon as the MN's uplink is associated with the corresponding MLD
proxy instance, multicast packets are forwarded again to the LMA and
eventually to receivers within the PMIP domain. (See the call flow
in Figure 2.) In this way, multicast source mobility is
transparently enabled in PMIPv6 domains that deploy the base scenario
for multicast.
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MN1 MAG1 MN2 MAG2 LMA
| | | | |
| | Mcast Data | | |
| |<---------------+ | |
| | Mcast Data | | |
| Join(G) +================================================>|
+--------------> | | | |
| Mcast Data | | | |
|<---------------+ | | |
| | | | |
| < Movement of MN 2 to MAG2 & PMIP Binding Update > |
| | | | |
| | |--- Rtr Sol -->| |
| | |<-- Rtr Adv ---| |
| | | | |
| | | < MLD Proxy Configuration > |
| | | | |
| | | (MLD Query) | |
| | |<--------------+ |
| | | Mcast Data | |
| | +-------------->| |
| | | | Mcast Data |
| | | +===============>|
| | | | |
| | Mcast Data | | |
| |<================================================+
| Mcast Data | | | |
|<---------------+ | | |
| | | | |
Legend: Rtr Sol - ICMPv6 Router Solicitation
Rtr Adv - ICMPv6 Router Advertisement
Figure 2: Call Flow for Group Communication in Multicast-Enabled PMIP
These multicast deployment considerations likewise apply for mobile
nodes that operate with their IPv4 stack enabled in a PMIPv6 domain.
PMIPv6 can provide IPv4 home address mobility support [RFC5844].
IPv4 multicast is handled by an IGMP proxy function at the MAG in an
analogous way.
Following these deployment steps, multicast traffic distribution
transparently interoperates with PMIPv6. It is worth noting that an
MN -- while being attached to the same MAG as the mobile source, but
associated with a different LMA -- cannot receive multicast traffic
on a shortest path. Instead, multicast streams flow up to the LMA of
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the mobile source, are transferred to the LMA of the mobile listener,
and are tunneled downwards to the MAG again. (See Section 5 for
further optimizations.)
3.2. Base Solution for Source Mobility: Details
Support of multicast source mobility in PMIPv6 requires that general
multicast functions be deployed at PMIPv6 routers and that their
interactions with the PMIPv6 protocol be defined as follows.
3.2.1. Operations of the Mobile Node
A mobile node willing to send multicast data will proceed as if
attached to the fixed Internet. No specific mobility or other
multicast-related functionalities are required at the MN.
3.2.2. Operations of the Mobile Access Gateway
A Mobile Access Gateway is required to have MLD proxy instances
deployed, one for each tunnel to an LMA, which serves as its unique
upstream link (cf. [RFC6224]). On the arrival of an MN, the MAG
decides on the mapping of downstream links to a proxy instance and
the upstream link to the LMA based on the regular Binding Update List
as maintained by PMIPv6 standard operations. When multicast data is
received from the MN, the MAG MUST identify the corresponding proxy
instance from the incoming interface and forwards multicast data
upstream according to [RFC4605].
The MAG MAY apply special admission control to enable multicast data
transmission from an MN. It is advisable to take special care that
MLD proxy implementations do not redistribute multicast data to
downstream interfaces without appropriate subscriptions in place.
3.2.3. Operations of the Local Mobility Anchor
For any MN, the Local Mobility Anchor acts as the persistent Home
Agent and at the same time as the default multicast upstream for the
corresponding MAG. It will manage and maintain a multicast
forwarding information base for all group traffic arriving from its
mobile sources. It SHOULD participate in multicast routing functions
that enable traffic redistribution to all adjacent LMAs within the
PMIPv6 domain and thereby ensure a continuous receptivity while the
source is in motion.
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3.2.3.1. Local Mobility Anchors Operating PIM
Local Mobility Anchors that operate the Protocol Independent
Multicast - Sparse Mode (PIM-SM) routing protocol [RFC4601] will
require sources to be directly connected for sending PIM registers to
the Rendezvous Point (RP). This does not hold in a PMIPv6 domain, as
MAGs are routers intermediate to the MN and the LMA. In this sense,
MNs are multicast sources external to the PIM-SM domain.
To mitigate this incompatibility common to all subsidiary MLD proxy
domains, the LMA MUST act as a PIM Border Router and activate the
Border-bit. In this case, the DirectlyConnected(S) is treated as
being TRUE for mobile sources and the PIM-SM forwarding rule "iif ==
RPF_interface(S)" is relaxed to be TRUE, as the incoming tunnel
interface from MAG to LMA is not considered part of the PIM-SM
component of the LMA (see Appendix A.1 of [RFC4601] ).
In addition, an LMA serving as the PIM Designated Router (DR) is
connected to MLD proxies via individual IP tunnel interfaces and will
experience changing PIM source states on handover. As the incoming
interface connects to a point-to-point link, PIM Assert contention is
not active, and incoming interface validation is only performed by
Reverse Path Forwarding (RPF) checks. Consequently, a PIM DR SHOULD
update incoming source states, as soon as RPF inspection succeeds,
i.e., after the PMIPv6 forwarding state update. Consequently, PIM
routers SHOULD be able to manage these state changes, but some
implementations are expected to incorrectly refuse packets until the
previous state has timed out.
Notably, running Bidirectional PIM (BIDIR-PIM) [RFC5015] on LMAs
remains robust with respect to source location and does not require
special configurations or state management for sources.
3.2.4. IPv4 Support
An MN in a PMIPv6 domain may use an IPv4 address transparently for
communication as specified in [RFC5844]. For this purpose, an LMA
can register an IPv4-Proxy-CoA in its Binding Cache, and the MAG can
provide IPv4 support in its access network. Correspondingly,
multicast membership management will be performed by the MN using
IGMP. For multicast support on the network side, an IGMP proxy
function needs to be deployed at MAGs in exactly the same way as for
IPv6. [RFC4605] defines IGMP proxy behavior in full agreement with
IPv6/MLD. Thus, IPv4 support can be transparently provided following
the obvious deployment analogy.
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For a dual-stack IPv4/IPv6 access network, the MAG proxy instances
SHOULD choose multicast signaling according to address configurations
on the link, but they MAY submit IGMP and MLD queries in parallel, if
needed. It should further be noted that the infrastructure cannot
identify two data streams as identical when distributed via an IPv4
and IPv6 multicast group. Thus, duplicate data may be forwarded on a
heterogeneous network layer.
The following points are worth noting about the scenario in [RFC5845]
in which overlapping private address spaces of different operators
can be hosted in a PMIP domain by using Generic Routing Encapsulation
(GRE) with key identification. This scenario implies that unicast
communication in the MAG-LMA tunnel can be individually identified
per MN by the GRE keys. This scenario still does not impose any
special treatment of multicast communication for the following
reasons.
Multicast streams from and to MNs arrive at a MAG on point-to-point
links (identical to unicast). Multicast data transmission from the
MAG to the corresponding LMA is link-local between the routers and
routing/forwarding remains independent of any individual MN. So, the
MAG-proxy and the LMA SHOULD NOT use GRE key identifiers, but plain
GRE in multicast communication (including MLD queries and reports).
Multicast traffic is transmitted using router-to-router forwarding
via the MAG-to-LMA tunnels and according to the MRIB of the MAG or
the LMA. It remains independent of MN's unicast addresses, while the
MAG proxy instance redistributes multicast data down the point-to-
point links (interfaces) according to its local subscription states,
independent of IP addresses of the MN.
3.2.5. Efficiency of the Distribution System
The distribution system of the base solution directly follows PMIPv6
routing rules and organizes multicast domains with respect to LMAs.
Thus, no coordination between address spaces or services is required
between the different instances, provided their associated LMAs
belong to disjoint multicast domains. Routing is optimal for
communication between MNs of the same domain or stationary
subscribers.
In the following situations, efficiency-related issues remain.
Multicast reception at LMA
In the current deployment scenario, the LMA will receive all
multicast traffic originating from its associated MNs. There is
no mechanism to suppress upstream forwarding in the absence of
receivers.
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MNs on the same MAG using different LMAs
For a mobile receiver and a source that use different LMAs, the
traffic has to go up to one LMA, cross over to the other LMA, and
then be tunneled back to the same MAG, causing redundant flows in
the access network and at the MAG.
These remaining deficits in routing efficiency can be resolved by
adding peering functions to MLD proxies as described in Section 5.
4. Direct Multicast Routing
There are deployment scenarios, where multicast services are
available throughout the access network independent of the PMIPv6
routing system [RFC7028]. In these cases, the visited networks grant
a local content distribution service (in contrast to LMA-based home
subscription) with locally optimized traffic flows. It is also
possible to deploy a mixed service model of local and LMA-based
subscriptions, provided that a unique way of service selection is
implemented. For example, access routers (MAGs) could decide on
service access based on the multicast address G or the source-
specific multicast (SSM) channel (S,G) under request. (See
Appendix A for further discussions.)
4.1. Overview
Direct multicast access can be supported by
o native multicast routing provided by one multicast router that is
neighboring MLD proxies deployed at MAGs within a flat access
network, or via tunnel uplinks,
o a multicast routing protocol such as PIM-SM [RFC4601] or BIDIR-PIM
[RFC5015] deployed at the MAGs.
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*** *** *** ***
* ** ** ** *
* *
* Multicast *
+----+ * Infrastructure * +----+
|LMA | * ** ** ** * |LMA |
+----+ *** *** *** *** +----+
| // \\ |
\\ // \\ PMIP (unicast) |
PMIP \\ // \\ // \\ ** *** *** ** //
(unicast) \\ // \\ // \\ * ** ** ** //
\\ // \\ // \\* Multicast *//
|| || || || * || Routing || *
+----+ +----+ * +----+ +----+ *
MLD Proxy |MAG1| |MAG2| * |MAG1| |MAG2| *
+----+ +----+ *+----+ ** ** +----+*
| | | | |*** *** ***|
| | | | | |
MN1 MN2 MN3 MN1 MN2 MN3
(a) Multicast Access at Proxy Uplink (b) Multicast Routing at MAG
Figure 3: Reference Networks for (a) Proxy-Assisted Direct Multicast
Access and (b) Dynamic Multicast Routing at MAGs
Figure 3 displays the corresponding deployment scenarios that
separate multicast from PMIPv6 unicast routing. It is assumed
throughout these scenarios that all MAGs (MLD proxies) are linked to
a single multicast routing domain. Notably, this scenario requires
coordination of multicast address utilization and service bindings.
Multicast traffic distribution can be simplified in these scenarios.
A single proxy instance at MAGs with uplinks into the multicast
domain will serve as a first-hop multicast gateway and avoid traffic
duplication or detour routing. Multicast routing functions at MAGs
will seamlessly embed access gateways within a multicast cloud.
However, mobility of the multicast source in this scenario will
require some multicast routing protocols to rebuild distribution
trees. This can cause significant service disruptions or delays (see
[RFC5757] for further aspects). Deployment details are specific to
the multicast routing protocol in use; this is described below for
common protocols.
4.2. MLD Proxies at MAGs
In a PMIPv6 domain, single MLD proxy instances can be deployed at
each MAG that enable multicast service at the access via an uplink to
a multicast service infrastructure (see Figure 3(a)). To avoid
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service disruptions on handovers, the uplinks of all proxies SHOULD
be adjacent to the same next-hop multicast router. This can either
be achieved by arranging proxies within a flat access network or by
using upstream tunnels that terminate at a common multicast router.
Multicast data submitted by a mobile source will reach the MLD proxy
at the MAG that subsequently forwards flows to the upstream and to
all downstream interfaces with appropriate subscriptions. Traversing
the upstream will transfer traffic into the multicast infrastructure
(e.g., to a PIM Designated Router) that will route packets to all
local MAGs that have joined the group, as well as further upstream
according to protocol procedures and forwarding states.
On handover, a mobile source will reattach to a new MAG and can
continue to send multicast packets as soon as PMIPv6 unicast
configurations have been completed. Like at the previous MAG, the
new MLD proxy will forward data upstream and downstream to
subscribers. Listeners local to the previous MAG will continue to
receive group traffic via the local multicast distribution
infrastructure following aggregated listener reports of the previous
proxy. In general, traffic from the mobile source continues to be
transmitted via the same next-hop multicast router using the same
source address and thus remains unchanged when seen from the wider
multicast infrastructure.
4.2.1. Considerations for PIM-SM on the Upstream
A mobile source that transmits data via an MLD proxy will not be
directly connected to a PIM Designated Router as discussed in
Section 3.2.3.1. Countermeasures apply correspondingly.
A PIM Designated Router that is connected to MLD proxies via
individual IP tunnel interfaces will experience invalid PIM source
states on handover. In some implementations of PIM-SM, this could
lead to an interim packet loss (see Section 3.2.3.1). This problem
can be mitigated by aggregating proxies on a lower layer.
4.2.2. SSM Considerations
Source-specific subscriptions invalidate with routes, whenever the
source moves from or to the MAG/proxy of a subscriber. Multicast
forwarding states will rebuild with unicast route changes. However,
this may lead to noticeable service disruptions for locally
subscribed nodes.
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4.3. PIM-SM at MAGs
The full-featured multicast routing protocol PIM-SM MAY be deployed
in the access network for providing multicast services in parallel to
unicast routes (see Figure 3(b)). Throughout this section, it is
assumed that the PMIPv6 mobility domain is part of a single PIM-SM
multicast routing domain with PIM-SM routing functions present at all
MAGs and all LMAs. The PIM routing instance at a MAG SHALL then
serve as the Designated Router (DR) for all directly attached Mobile
Nodes. For expediting handover operations, it is advisable to
position PIM Rendezvous Points (RPs) in the core of the PMIPv6
network domain. However, regular IP routing tables need not be
present in a PMIPv6 deployment, and additional effort is required to
establish reverse path forwarding rules as required by PIM-SM.
4.3.1. Routing Information Base for PIM-SM
In this scenario, PIM-SM will rely on a Multicast Routing Information
Base (MRIB) that is generated independently of the policy-based
routing rules of PMIPv6. The granularity of mobility-related routing
locators required in PIM depends on the complexity (specific phase)
of its deployment.
For all three phases in the operation of PIM (see [RFC4601]), the
following information is needed.
o All routes to networks and nodes (including RPs) that are not
mobile members of the PMIPv6 domain MUST be defined consistently
among PIM routers and MUST remain unaffected by node mobility.
The setup of these general routes is expected to follow the
topology of the operator network and is beyond the scope of this
document.
The following route entries are required at a PIM-operating MAG when
phase two or three of PIM or PIM-SSM is in operation.
o Local routes to the Home Network Prefixes (HNPs) of all MNs
associated with their corresponding point-to-point attachments
that MUST be included in the local MRIB.
o All routes to MNs that are attached to distant MAGs of the PMIPv6
domain point towards their corresponding LMAs. These routes MUST
be made available in the MRIB of all PIM routers (except for the
local MAG of attachment), but they MAY be eventually expressed by
an appropriate default entry.
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4.3.2. Operations of PIM in Phase One (RP Tree)
A new mobile source S will transmit multicast data of group G towards
its MAG of attachment. Acting as a PIM DR, the access gateway will
unicast-encapsulate the multicast packets and forward the data to the
Virtual Interface (VI) with encapsulation target RP(G), a process
known as "PIM source registering". The RP will decapsulate and
natively forward the packets down the RP-based distribution tree
towards (mobile and stationary) subscribers.
On handover, the point-to-point link connecting the mobile source to
the old MAG will go down and all (S,*) flows terminate. In response,
the previous DR (MAG) deactivates the data encapsulation channels for
the transient source (i.e., all DownstreamJPState(S,*,VI) are set to
NoInfo state). After reattaching and completing unicast handover
negotiations, the mobile source can continue to transmit multicast
packets, while being treated as a new source at its new DR (MAG).
Source register encapsulation will be immediately initiated, and
(S,G) data continue to flow natively down the (*,G) RP-based tree.
Source handover management in PIM phase one admits low complexity and
remains transparent to receivers. In addition, the source register
tunnel management of PIM is a fast protocol operation that introduces
little overhead. In a PMIPv6 deployment, PIM RPs MAY be configured
to uninitiated (S,G) shortest path trees for mobile sources, and thus
remain in phase one of the protocol. The price to pay for such
simplified deployment lies in possible routing detours by an overall
RP-based packet distribution.
4.3.3. Operations of PIM in Phase Two (Register-Stop)
After receiving source register packets, a PIM RP eventually will
initiate a source-specific Join for creating a shortest path tree to
the (mobile) source S and issue a source register stop at the native
arrival of data from S. For initiating an (S,G) tree, the RP, as
well as all intermediate routers, require route entries for the HNP
of the MN that -- unless the RP coincides with the MAG of S -- point
towards the corresponding LMA of S. Consequently, the (S,G) tree
will proceed from the RP via the (stable) LMA, down the LMA-MAG
tunnel to the mobile source. This tree can be of lower routing
efficiency than the PIM source register tunnel established in phase
one.
On handover, the mobile source reattaches to a new MAG (DR), and
PMIPv6 unicast management will transfer the LMA-MAG tunnel to the new
point of attachment. However, in the absence of a corresponding
multicast forwarding state, the new DR will treat S as a new source
and initiate a source registering of PIM phase one with the RP. In
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response, the PIM RP will recognize the known source at a new
(tunnel) interface and will immediately respond with a register stop.
As the RP had previously joined the shortest path tree towards the
source via the LMA, it will see an RPF change when data arrives at a
new interface. This is implementation dependent and can trigger an
update of the PIM MRIB as well as a new PIM Join message that will
install the multicast forwarding state missing at the new MAG.
Otherwise, the tree is periodically updated by Joins transmitted
towards the new MAG on a path via the LMA. In proceeding this way, a
quick recovery of PIM transition from phase one to two will be
performed per handover.
4.3.4. Operations of PIM in Phase Three (Shortest-Path Tree)
In response to an exceeded threshold of packet transmission, DRs of
receivers eventually will initiate a source-specific Join for
creating a shortest path tree to the (mobile) source S, thereby
transitioning PIM into the final shortcut phase three. For all
receivers not sharing a MAG with S, this (S,G) tree will range from
the receiving DR via the (stable) LMA, the LMA-MAG tunnel, and the
serving MAG to the mobile source. This tree is of higher routing
efficiency than that established in the previous phase two, but it
need not outperform the PIM source register tunnel established in
phase one. It provides the advantage of immediate data delivery to
receivers that share a MAG with S.
On handover, the mobile source reattaches to a new MAG (DR), and
PMIPv6 unicast management will transfer the LMA-MAG tunnel to the new
point of attachment. However, in the absence of a corresponding
multicast forwarding state, the new DR will treat S as a new source
and initiate a source registering of PIM phase one. A PIM
implementation compliant with this change can recover phase three
states in the following way. First, the RP recovers to phase two as
described in the previous section and will not forward data arriving
via the source register tunnel. Tree maintenance eventually
triggered by the RPF change (see Section 4.3.3) will generate proper
states for a native forwarding from the new MAG via the LMA.
Thereafter, packets arriving at the LMA without source register
encapsulation are forwarded natively along the shortest path tree
towards receivers.
In consequence, the PIM transitions from phase one to two to three
will be quickly recovered per handover but still lead to an enhanced
signaling load and intermediate packet loss.
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4.3.5. PIM-SSM Considerations
Source-specific Joins of receivers will guide PIM to operate in SSM
mode and lead to an immediate establishment of source-specific
shortest path trees. Such (S,G) trees will equal the distribution
system of PIM's final phase three (see Section 4.3.4). However, on
handover and in the absence of RP-based data distribution, SSM data
delivery cannot be resumed via source registering as in PIM phase
one. Consequently, data packets transmitted after a handover will be
discarded at the MAG until regular tree maintenance has reestablished
the (S,G) forwarding state at the new MAG.
4.3.6. Handover Optimizations for PIM
Source-specific shortest path trees are constructed in PIM-SM (phase
two and three) and in PIM-SSM. These RPF-trees traverse LMA-MAG
tunnels towards a source. As PIM remains unaware of source mobility
management, these trees invalidate under handovers with each tunnel
re-establishment at a new MAG. Regular tree maintenance of PIM will
recover the states, but it remains unsynchronized and too slow to
seamlessly preserve PIM data distribution services.
A method to quickly recover PIM (S,G) trees under handover SHOULD
synchronize multicast state maintenance with unicast handover
operations and can proceed as follows. On handover, an LMA reads all
(S,G) Join states from its corresponding tunnel interface and
identifies those source addresses S_i that match moving HNPs. After
re-establishing the new tunnel, it SHOULD associate the (S_i,*) Join
states with the new tunnel endpoint and immediately trigger a state
maintenance (PIM Join) message. In proceeding this way, the source-
specific PIM states are transferred to the new tunnel endpoint and
propagated to the new MAG in synchrony with unicast handover
procedures.
4.4. BIDIR-PIM
BIDIR-PIM MAY be deployed in the access network for providing
multicast services in parallel to unicast routes. Throughout this
section, it is assumed that the PMIPv6 mobility domain is part of a
single BIDIR-PIM multicast routing domain with BIDIR-PIM routing
functions present at all MAGs and all LMAs. The PIM routing instance
at a MAG SHALL then serve as the Designated Forwarder (DF) for all
directly attached Mobile Nodes. For expediting handover operations,
it is advisable to position BIDIR-PIM Rendezvous Point Addresses
(RPAs) in the core of the PMIPv6 network domain. As regular IP
routing tables need not be present in a PMIPv6 deployment, reverse
path forwarding rules as required by BIDIR-PIM need to be
established.
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4.4.1. Routing Information Base for BIDIR-PIM
In this scenario, BIDIR-PIM will rely on a Multicast Routing
Information Base (MRIB) that is generated independently of the
policy-based routing rules of PMIPv6. The following information is
needed.
o All routes to networks and nodes (including RPAs) that are not
mobile members of the PMIPv6 domain MUST be defined consistently
among BIDIR-PIM routers and remain unaffected by node mobility.
The setup of these general routes is expected to follow the
topology of the operator network and is beyond the scope of this
document.
4.4.2. Operations of BIDIR-PIM
BIDIR-PIM will establish spanning trees across its network domain in
conformance to its pre-configured RPAs and the routing information
provided. Multicast data transmitted by a mobile source will
immediately be forwarded by its DF (MAG) onto the spanning tree for
the multicast group without further protocol operations.
On handover, the mobile source reattaches to a new MAG (DF), which
completes unicast network configurations. Thereafter, the source can
immediately proceed with multicast packet transmission onto the pre-
established distribution tree. BIDIR-PIM does not require protocol
signaling or additional reconfiguration delays to adapt to source
mobility, and it can be considered the protocol of choice for mobile
multicast operations in the access network. As multicast streams
always flow up to the Rendezvous Point Link, some care should be
taken to configure RPAs compliant with network capacities.
5. MLD Proxy Peering Function for Optimized Source Mobility in PMIPv6
A deployment of MLD proxies (see [RFC4605]) at MAGs has proven a
useful and appropriate approach to multicast in PMIPv6; see [RFC6224]
and [RFC7028]. However, deploying unmodified standard proxies can go
along with significant performance degradation for mobile senders as
discussed in this document. To overcome these deficits, an optimized
approach to multicast source mobility based on extended peering
functions among proxies is defined in this section. Based on such
direct data exchange between proxy instances at MAGs, triangular
routing is avoided and multicast streams can be disseminated directly
within a PMIPv6 access network, and in particular within MAG routing
machines. Prior to presenting the solution, we will summarize the
relevant requirements.
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5.1. Requirements
Solutions that extend MLD proxies by additional uplinking functions
need to comply to the following requirements.
Prevention of routing loops
In the absence of a full-featured routing logic at an MLD proxy,
simple and locally decidable rules need to prevent source traffic
from traversing the network in loops that would be potentially
enabled by multiple uplinks.
Unique coverage of receivers
Listener functions at proxies require simple, locally decidable
rules to initiate a unique delivery of multicast packets to all
receivers.
Following local filtering techniques, these requirements are met in
the following solution.
5.2. Overview
A peering interface for MLD proxies allows for a direct data exchange
of locally attached multicast sources. Such peering interfaces can
be configured -- as a direct link or a bidirectional tunnel --
between any two proxy instances (locally deployed as in [RFC6224] or
remotely deployed). Peerings remain as silent virtual links in
regular proxy operations. Data is exchanged on such links only in
cases where one peering proxy on its downstream directly connects to
a source of multicast traffic to which the other peering proxy
actively subscribes. In such cases, the proxy connected to the
source will receive a listener report on its peering interface and
will forward traffic from its local source accordingly. It is worth
noting that multicast traffic distribution on peering links does not
follow reverse unicast paths to sources. In the following,
operations are defined for Any-Source Multicast (ASM) and SSM, but
they provide superior performance in the presence of source-specific
signaling (IGMPv3/MLDv2) [RFC4604].
5.3. Operations in Support of Multicast Senders
An MLD proxy with the perspective of a sender will see peering
interfaces as restricted downstream interfaces. It will install and
maintain source filters at its peering links that will restrict data
transmission to those packets that originate from a source that is
locally attached at one of its downstream interfaces.
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In detail, a proxy will extract from its configuration the network
prefixes attached to its downstream interfaces and MUST implement a
source filter base at its peering interfaces that restricts data
transmission to IP source addresses from its local prefixes. This
filter base MUST be updated if and only if the downstream
configuration changes (e.g., due to mobility). Multicast packets
that arrive from the upstream interface of the proxy are thus
prevented from traversing any peering link, but they are only
forwarded to regular downstream interfaces with appropriate
subscription states. In this way, multihop forwarding on peering
links is prevented.
Multicast traffic arriving from a locally attached source will be
forwarded to the regular upstream interface and all downstream
interfaces with appropriate subscription states (i.e., regular proxy
operations). In addition, multicast packets of local origin are
transferred to those peering interfaces with appropriate subscription
states.
5.4. Operations in Support of Multicast Listeners
On the listener side, peering interfaces appear as preferred upstream
links. The multicast proxy will attempt to receive multicast
services on peering links for as many groups (channels) as possible.
The general upstream interface configured according to [RFC4605] will
be used only for retrieving those groups (channels) that remain
unavailable from peerings. From this extension of [RFC4605], an MLD
proxy with peering interconnects will exhibit several interfaces for
pulling remote traffic: the regular upstream and the peerings.
Traffic available from any of the peering links will be mutually
disjoint but normally also available from the upstream. To prevent
duplicate traffic from arriving at the listener side, the proxy
o MAY delay aggregated reports to the upstream, and
o MUST apply appropriate filters to exclude duplicate streams.
In detail, an MLD proxy instance at a MAG first issues listener
reports (in parallel) to all of its peering links. These links span
at most one (virtual) hop. Whenever certain group traffic (SSM
channels) does not arrive from the peerings after a waiting time
(default: 10 ms (node-local) and 25 ms (remote)), additional reports
(complementary reports, in the case of SSM) are sent to the standard
upstream interface.
Whenever traffic from a peering link arrives, an MLD proxy MUST
install source filters at its upstream interfaces (as described in
RFC 4605) in the following way.
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ASM with IGMPv2/MLDv1: In the presence of ASM using IGMPv2/MLDv1,
only, the proxy cannot signal source filtering to its upstream.
Correspondingly, it applies (S,*) ingress filters at its upstream
interface for all sources S seen in traffic on the peering links.
It is noteworthy that unwanted traffic is still replicated to the
proxy via the (wired) provider backbone, but it is not forwarded
into the wireless access network.
ASM with IGMPv3/MLDv2: In the presence of source-specific signaling
(IGMPv3/MLDv2), the upstream interface is set to (S,*) exclude
mode for all sources S seen in traffic of the peering links. The
corresponding source-specific signaling will prevent forwarding of
duplicate traffic throughout the access network.
SSM: In the presence of Source-Specific Multicast, the proxy will
subscribe on its uplink interface to those (S,G) channels, only,
that do not arrive via the peering links.
MLD proxies will install data-driven timers (source-timeout) for each
source but common to all peering interfaces to detect interruptions
of data services from individual sources at proxy peers. Termination
of source-specific flows may be application specific, but also may be
due to a source handover or a transmission failure. After a
handover, a mobile source may reattach at another MLD proxy with a
peering relation to the listener, or at a proxy that does not peer.
While in the first case, traffic reappears on another peering link;
in the second case, data can only be retrieved via the regular
upstream. To account for the latter, the MLD proxy revokes the
source-specific filter(s) at its upstream interface, after the
source-timeout expires (default: 50 ms). Corresponding traffic will
then be pulled from the regular upstream interface. Source-specific
filters MUST be reinstalled whenever traffic of this source arrives
at any peering interface.
There is a noteworthy trade-off between traffic minimization and
available traffic at the upstream that is locally filtered at the
proxy. Implementors can use this relation to optimize for service-
specific requirements.
In proceeding this way, multicast group data will arrive from peering
interfaces first, while only peer-wise unavailable traffic is
retrieved from the regular upstream interface.
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6. Security Considerations
This document defines multicast sender mobility based on PMIPv6 and
common multicast routing protocols. Consequently, threats identified
as security concerns in [RFC2236], [RFC2710], [RFC3810], [RFC4605],
[RFC5213], and [RFC5844] are inherited by this document.
In addition, particular attention should be paid to implications of
combining multicast and mobility management at network entities. As
this specification allows mobile nodes to initiate the creation of
multicast forwarding states at MAGs and LMAs while changing
attachments, threats of resource exhaustion at PMIP routers and
access networks arise from rapid state changes, as well as from high-
volume data streams routed into access networks of limited
capacities. In cases of PIM-SM deployment, handover operations of
the MNs include re-registering sources at the Rendezvous Points at
possibly high frequency. In addition to proper authorization checks
of MNs, rate controls at routing agents and replicators may be needed
to protect the agents and the downstream networks. In particular,
MLD proxy implementations at MAGs SHOULD automatically erase
multicast state on the departure of MNs, as mobile multicast
listeners in the PMIPv6 domain will in general not actively terminate
group membership prior to departure.
The deployment of IGMP/MLD proxies for multicast routing requires
particular care, as routing loops on the upstream are not
automatically detected. Peering functions between proxies extend
this threat in the following way. Routing loops among peering and
upstream interfaces are prevented by filters on local sources. Such
filtering can fail whenever prefix configurations for downstream
interfaces at a proxy are incorrect or inconsistent. Consequently,
implementations of peering-enabled proxies SHOULD take particular
care on keeping IP configurations consistent at the downstream in a
reliable and timely manner. (See [RFC6224] for requirements on
PMIPv6-compliant implementations of MLD proxies.)
7. Acknowledgements
The authors would like to thank (in alphabetical order) David Black,
Luis M. Contreras, Spencer Dawkins, Muhamma Omer Farooq, Bohao Feng,
Sri Gundavelli, Dirk von Hugo, Ning Kong, Jouni Korhonen, He-Wu Li,
Cong Liu, Radia Perlman, Akbar Rahman, Behcet Sarikaya, Stig Venaas,
Li-Li Wang, Sebastian Woelke, Qian Wu, and Zhi-Wei Yan for advice,
help, and reviews of the document. Funding by the German Federal
Ministry of Education and Research within the G-LAB Initiative
(projects HAMcast, Mindstone, and SAFEST) is gratefully acknowledged.
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710, October
1999.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, August 2006.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, October 2007.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
[RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
Mobile IPv6", RFC 5844, May 2010.
[RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
in IPv6", RFC 6275, July 2011.
8.2. Informative References
[MULTI-EXT]
Schmidt, T., Ed., Waehlisch, M., Koodli, R., Fairhurst,
G., and D. Liu, "Multicast Listener Extensions for MIPv6
and PMIPv6 Fast Handovers", Work in Progress, May 2014.
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[PEERING-ANALYSIS]
Schmidt, TC., Woelke, S., and M. Waehlisch, "Peer my Proxy
- A Performance Study of Peering Extensions for Multicast
in Proxy Mobile IP Domains", Proc. of 7th IFIP Wireless
and Mobile Networking Conference (WMNC 2014), IEEE Press,
May 2014.
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, November 1997.
[RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Protocol Version 2 (MLDv2) for Source-
Specific Multicast", RFC 4604, August 2006.
[RFC5757] Schmidt, T., Waehlisch, M., and G. Fairhurst, "Multicast
Mobility in Mobile IP Version 6 (MIPv6): Problem Statement
and Brief Survey", RFC 5757, February 2010.
[RFC5845] Muhanna, A., Khalil, M., Gundavelli, S., and K. Leung,
"Generic Routing Encapsulation (GRE) Key Option for Proxy
Mobile IPv6", RFC 5845, June 2010.
[RFC6224] Schmidt, T., Waehlisch, M., and S. Krishnan, "Base
Deployment for Multicast Listener Support in Proxy Mobile
IPv6 (PMIPv6) Domains", RFC 6224, April 2011.
[RFC7028] Zuniga, JC., Contreras, LM., Bernardos, CJ., Jeon, S., and
Y. Kim, "Multicast Mobility Routing Optimizations for
Proxy Mobile IPv6", RFC 7028, September 2013.
[RFC7161] Contreras, LM., Bernardos, CJ., and I. Soto, "Proxy Mobile
IPv6 (PMIPv6) Multicast Handover Optimization by the
Subscription Information Acquisition through the LMA
(SIAL)", RFC 7161, March 2014.
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Appendix A. Multiple Upstream Interface Proxy
In this section, we document upstream extensions for an MLD proxy
that were originally developed during the work on this document.
Multiple proxy instances deployed at a single MAG (see Section 3) can
be avoided by adding multiple upstream interfaces to a single MLD
proxy. In a typical PMIPv6 deployment, each upstream interface of a
single proxy instance can interconnect to one of the LMAs. With such
ambiguous upstream options, appropriate forwarding rules MUST be
supplied to
o unambiguously guide traffic forwarding from directly attached
mobile sources, and
o lead listener reports to initiating unique traffic subscriptions.
This can be achieved by a complete set of source- and group-specific
filter rules (e.g., (S,*), (*,G)) installed at proxy interfaces.
These filters MAY be derived in part from PMIPv6 routing policies and
can include a default behavior (e.g., (*,*)).
A.1. Operations for Local Multicast Sources
Packets from a locally attached multicast source will be forwarded to
all downstream interfaces with appropriate subscriptions, as well as
up the interface with the matching source-specific filter.
Typically, the upstream interface for a mobile multicast source is
chosen based on the policy routing (e.g., the MAG-LMA tunnel
interface for LMA-based routing or the interface towards the
multicast router for direct routing), but alternate configurations
MAY be applied. Packets from a locally attached multicast source
will be forwarded to the corresponding upstream interface with the
matching source-specific filter, as well as all the downstream
interfaces with appropriate subscriptions.
A.2. Operations for Local Multicast Subscribers
Multicast listener reports are group-wise aggregated by the MLD
proxy. The aggregated report is issued to the upstream interface
with a matching group/channel-specific filter. The choice of the
corresponding upstream interface for aggregated group membership
reports MAY be additionally based on some administrative scoping
rules for scoped multicast group addresses.
In detail, a Multiple Upstream Interface proxy will provide and
maintain a Multicast Subscription Filter Table that maps source- and
group-specific filters to upstream interfaces. The forwarding
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decision for an aggregated MLD listener report is based on the first
matching entry from this table, with the understanding that for
IGMPv3/MLDv2 the MLD proxy performs a state decomposition, if needed
(i.e., a (*,G) subscription is split into (S,G) and (* \ S,G) in the
presence of (*,G) after (S,G) interface entries), and that
(S,*)-filters are always false in the absence of source-specific
signaling, i.e., in IGMPv2/MLDv1 only domains.
In typical deployment scenarios, specific group services (channels)
are either
o associated with selected uplinks to remote LMAs, while a (*,*)
default subscription entry (in the last table line) is bound to a
local routing interface, or
o configured as local services first, while a (*,*) default entry
(in the last table line) points to a remote uplink that provides
the general multicast support.
Appendix B. Implementation
An implementation of the extended IGMP/MLD proxy has been provided
within the MCPROXY project (http://mcproxy.realmv6.org/). This open-
source software is written in C++ and uses forwarding capabilities of
the Linux kernel. It supports all regular operations according to
[RFC4605] and allows for multiple proxy instances on one node,
dynamically changing downstream links, proxy-to-proxy peerings, and
multiple upstream links with individual configurations. The software
can be downloaded from GitHub at
<https://github.com/mcproxy/mcproxy>. Based on this software, an
experimental performance evaluation of the proxy peering function has
been reported in [PEERING-ANALYSIS].
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Authors' Addresses
Thomas C. Schmidt (editor)
HAW Hamburg
Berliner Tor 7
Hamburg 20099
Germany
EMail: schmidt@informatik.haw-hamburg.de
URI: http://inet.cpt.haw-hamburg.de/members/schmidt
Shuai Gao
Beijing Jiaotong University
Beijing
China
EMail: shgao@bjtu.edu.cn
Hong-Ke Zhang
Beijing Jiaotong University
Beijing
China
EMail: hkzhang@bjtu.edu.cn
Matthias Waehlisch
link-lab & FU Berlin
Hoenower Str. 35
Berlin 10318
Germany
EMail: mw@link-lab.net
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